Lab talk

Jun 14, 2012

Study compares light trapping in hexagonal and square nano arrays

Understanding the interaction of incident light with nano-, or subwavelength-structures is of particular importance to guide the structural design of high-efficiency photoelectric devices, such as advanced nanowire/pillar array-based solar cells and photo detectors. Extensive studies by different groups over the past 5 years have led to several viewpoints on the enhancement mechanisms taking place – for example, scattering-induced absorption enhancement and wave-guided mode-based enhancement. Clarifying the debate is not just of fundamental scientific interest, but also carries important practical value.

A team from Nanyang Technological University, Singapore, has conducted a detailed study, which employs a full wave finite element method and hexagonally arranged Si nanopillar/wire arrays. The aim is to clearly describe the interaction process between incident light and nano-structures, and to clarify the primary mechanism responsible for the enhancement in light absorption.

The scientists found that the wave-guided modes formed at some designated wavelengths do increase light trapping to some extent at the base of the scattering-based absorption enhancement region, but do not affect the change trend of light trapping capability with the Si nanopillar length.

Furthermore, the team compared the light absorption behaviors of Si nanopillar arrays with different arrangement schemes, and found that there is little impact of the array symmetry on the light trapping capability.

The researchers point out that for the Si nanowire test samples prepared using both bottom up and top down paradigms, the microstructures are not as uniform as the features used for modelling, which will affect the formation of waveguide modes. As a result, scattering-induced light absorption enhancement is likely to become the main consideration when fabricating devices.

About the author

Dr Junshuai Li was a Research Fellow at Nanyang Technology University, Singapore and presently holds a faculty position at Lanzhou University, China. His research interests focus on the design and fabrication of nano surface textures for highly efficient ultrathin film-based solar cells, and also on the optical and electrical characterization of nanostructures.